1. Field of the Invention
The invention relates to a method of determining the risk of ice deposition due to precipitation. The invention is particularly, but not exclusively intended for use in connection with determination of the risk of icing in connection with air traffic.
2. The Prior Art
When there is a risk of ice formation, the air traffic uses anti-icing liquids of various types and concentrations, and the problem is to estimate for how long the anti-icing liquid will stay effective during the existing weather conditions. This is referred to as ‘holdover time’; in the following designated ‘HOT’.
The international airline organisations publish tables that indicate a time interval for holdover time for some anti-icing liquids and for quite a small number of concentrations thereof. These tables, the only tool available at present, are associated with two major factors of uncertainty. Firstly the time intervals listed in the tables are given with large margins, eg a minimum of 30 and a maximum of 60 minutes, and secondly the tables can be used only if it is possible to correctly estimate the precipitation, the tables being divided in accordance with types of precipitation, such as eg snow or super-cooled water. The final responsibility for the estimation lies with the pilot, ie that from within the cockpit, frequently in weather conditions such as following winds and through a heavily heated slanted window, he is to estimate the type of precipitation and then take a stand on the minimum and maximum time intervals given in the table.
The very varying types of precipitation that typically occur within the temperature range of from 5° C. and 8° C. above freezing point are the cause of the longest delays in the airports and often the planes must wait long to obtain permission to take off, while the anti-icing liquid is consumed more quickly or slowly in response to the precipitation conditions.
To date, 141 aircraft accidents have been ascribed to ice accumulation with an ensuing death toll of 1200.
It is the object of the invention to provide a method that enables determination of HOT, wherein the determination is based on actual measurements rather than the subjective estimations resorted to so far in the prior art.